Strenuous means requiring great effort, energy, or exertion. A strenuous hike involves steep climbs that leave you breathing hard and your legs burning. Strenuous exercise, like running sprints or doing pushups, demands serious physical work. The word applies to both physical and mental activities: you might have a strenuous day at school filled with difficult tests and challenging projects, or make a strenuous effort to master a tricky piano piece.

When something is strenuous, it pushes you. It makes you work harder than usual and often leaves you tired afterward. Carrying heavy boxes up three flights of stairs is strenuous. So is studying intensely for hours, or objecting strenuously to an unfair rule.

The word often appears in the phrase strenuous objection, meaning a forceful, energetic disagreement. A lawyer might make a strenuous objection in court, or you might strenuously object to an unfair rule. In these cases, strenuous describes the intensity and vigor of the effort, whether physical or mental. Something strenuous demands your full commitment and leaves no room for halfhearted attempts.